LOWELL, Mass. — Donald Trump said in an interview that rival Ted Cruz’s Canadian birthplace was a “very precarious” issue that could make the Texas senator vulnerable if he became the Republican presidential nominee.

“Republicans are going to have to ask themselves the question: ‘Do we want a candidate who could be tied up in court for two years?’ That’d be a big problem,” Trump said when asked about the topic. “It’d be a very precarious one for Republicans because he’d be running and the courts may take a long time to make decision. You don’t want to be running and have that kind of thing over your head.”

Trump added, “I’d hate to see something like that get in his way. But a lot of people are talking about it, and I know that even some states are looking at it very strongly, the fact that he was born in Canada and he has had a double passport.”

Catherine Frazier, a spokeswoman for Cruz, declined to comment Tuesday.

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Trump’s remarks — part of a backstage interview before a rally here Monday night — come as Cruz is rising as a serious threat in the presidential campaign, especially in Iowa, where some polls have shown Cruz eclipsing the billionaire mogul. The two have had a cordial, at times even friendly relationship over the past year, but they are competing intensely for the support of conservatives as the Feb. 1 Iowa caucuses draw near.

There have been recent signs of tension. At a rally last month in Iowa, Trump told voters of Cruz, “Just remember this — you’ve got to remember, in all fairness, to the best of my knowledge, not too many evangelicals come out of Cuba, okay? Just remember that ... just remember.”

In the Post interview, Trump insisted that he was providing a candid assessment of his leading opponent rather than initiating a personal attack and reviving the so-called “birther” debate that he once led against President Obama. He repeatedly said he is hearing chatter on the topic among voices on the right. “People are bringing it up,” he said.

The Constitution requires presidents to be a “natural-born citizen.” Anyone born to a U.S. citizen is granted citizenship under current U.S. law, regardless of where the birth takes place.

Cruz’s mother was a U.S. citizen when he was born in Calgary in 1970; his father was born in Cuba. Cruz has long said that because his mother is a citizen by birth, he is one as well and fits under the definition of a natural-born citizen. Since his election to the Senate, Cruz has released his birth certificate and renounced his Canadian citizenship.

Legal scholars agree that Cruz meets the Constitution’s natural-born citizenship requirement, though it is untested in the courts.

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Several previous presidential candidates have run for office with similar backgrounds, such as Sen. John McCain of Arizona, the 2008 Republican nominee, who was born in the Panama Canal Zone to U.S. citizens.

In the interview, Trump alluded to an ongoing lawsuit in Vermont where a man is trying to keep three Republican presidential candidates, including Cruz, off the ballot. According to The Rutland Herald, the lawsuit names state officials as defendants.

Trump has long flirted with “birtherism,” questioning Obama’s love of country and legal claim to the presidency. He supported efforts to investigate Obama’s birth in Hawaii and often suggested that the president was born outside the country.

Trump’s crusade reached its zenith in 2011, when Obama felt obliged to publicly release his long-form birth certificate. The president then mocked Trump over the issue at the White House Correspondents Dinner that year. Since then, Trump has quieted his speculation about Obama’s birth — while still declining to accept Obama’s legitimacy.